1. Field of the Invention
The present invention relates to an earphone and, in particular, to an earphone that has an insertion part to be inserted in the external auditory canal of a user.
2. Description of the Related Art
Among various earphones on the market today, there are, for instance, canal type (earplug type) earphones with which the user hears sounds output from an audio output unit thereof, with the earpiece or the like inserted in the external auditory canal. And proposed for such canal type earphones are sound-insulating earphones, which includes an elongated earphone wrapped in a sound-insulating elastic member in order to prevent the leak of sound out of the ear. Also proposed are piezoelectric earphones having, for example, a piezoelectric acoustic member within an insertion tube to be inserted in the external auditory canal in order to make a sound generating portion located outside the external auditory canal smaller.
In recent years, the broadening use of portable music players has been accelerating the development of canal type earphones capable of outputting sounds of excellent quality. However, as is described in the above-cited references, locating the audio output unit inside the external auditory canal gives rise to the necessity to make the audio output unit smaller. Generally, the smaller the audio output unit is, the more difficult it will be to output sounds of better quality. Hence, in locating the audio output unit inside the external auditory canal, the problem to be addressed is to suppress the quality loss of sounds output therefrom.